python-expression 0.1

Serialize and deserialize nested compound expression strings such as (a = 1 or (b = 2 and c = 3)) into parsable expression graphs such as [ key:a operator:= value:1, conjunction:or, [ key:b operator:= value:2, conjunction:and, key:c operator:= value:3 ] ].

Expression

About

Serialize and deserialize nested compound expression strings such as (a = 1 or (b = 2 and c = 3)) into parsable expression trees such as [key:a operator:= value:1, conjunction:or, [key:b operator:= value:2, conjunction:and, key:c operator:= value:3]].

You may want to:-

• provide an easy to configure filter on an endpoint such as GET /services?filter=(price lt 200 and duration is 2hrs).
• build an ORM filter based on the expression.
• simply evaluate that an expression is True or False.

These sets of classes make few assumptions as to how conditions will be evaluated. It lets the author configure handlers that can be used to resolve conditions.

Install

• Todo

Configure

Use

Deserialize a string into a tree of conditions.

expression = Expression('(a = 1 and b = 2)')
conditions = expression.to_conditions()

print(conditions.conditions[0].key))        # a
print(conditions.conditions[0].operator))   # =
print(conditions.conditions[0].value))      # 1

print(conditions.conditions[1].value))      # and

print(conditions.conditions[2].key)))       # b
print(conditions.conditions[2].operator))   # =
print(conditions.conditions[2].value))      # 2

Evaluate an expression such date date_between 2020-09-26,2020-09-28 as a boolean.

Instantiate the Evaluate object, passing through resolved expression arguments. In this case the date key will be resolved to a date object of 2020-09-27.

evaluate = Evaluate({
    "date": datetime.strptime("2020-09-27", '%Y-%M-%d')
})

Before evaluating ensure that the date_between expression can be handled by a designated Handler such as DateBetweenHandler.

evaluate.add_condition_handlers({
    'date_between': DateBetweenHandler
})

Now evaluate the expression from string.

result = evaluate.from_expression('date date_between 2020-09-26,2020-09-28')
self.assertTrue(result)

You can plug in any custom handler to suit the usecase.

class DateBetweenHandler(Handler):

    def handle(self, condition):
        key = self._data.get(condition.key)

        values = condition.value.split(',')
        date1 = datetime.strptime(values[0], '%Y-%M-%d')
        date2 = datetime.strptime(values[1], '%Y-%M-%d')

        return date1 <= key <= date2

Contribute

Running tests

coverage run -m unittest2 discover -p="*Test.py"
coverage html

or use

bash bin/run-tests

bash bin/run-tests *Test.py